Browsing by Author "Lasich, Matthew."

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Monte Carlo simulations of systems of light alcohols + water + n-dodecane and water solubility and structures in polytetrafluoroethylene.
(2011) Lasich, Matthew.; Ramjugernath, Matthew.
Polytetrafluoroethylene (Teflon®) is encountered in many environments – frying pans, clothing, osmotic distillation membranes, to name a few – yet the solubility and clustering behaviour of water with this material was not found in the open literature. This information may be useful in applications where an absence of water is desired, such as in clothing and textiles. Previous work on polyethylene + water has shown that small water clusters form in the amorphous portion of the polymer. This work investigated this phenomenon for the case of polytetrafluoroethylene + water. Initially, a test system of light alcohols + water + n-dodecane was investigated using Gibbs Ensemble Monte Carlo simulations and compared to previous laboratory experiments. This test system was investigated in order to gain expertise in the methodologies and theory behind Monte Carlo simulation, as well as to gain experience with using the necessary software. For this test system, it was found that the TraPPE parameters representing the interactions between the alcohols and the n-dodecane were not adequate and lead to increasing deviations with increasing carbon number in the alcohol. To replicate the conditions of the amorphous polymer matrix, liquid-liquid equilibrium between water and the polymer was investigated. Gibbs Ensemble Monte Carlo simulations have been performed for systems of perfluoroalkanes and water to determine the influence of temperature and carbon number on the solubility and clustering behaviour of water within the perfluoroalkanes. The temperature range in this study was from 450 K to 600 K, and the perfluoroalkane carbon number range was from 8 to 300 carbon atoms. With increasing carbon number, it was found that there was an asymptotic value of 98.0 mole percent water in the polymer phase. With increasing temperatures it was found that there were exponential increases in solubility of water into the polymer matrix. Previous work on clustering and supramolecular structure of perfluoroalkanes described the rigidity of the perfluoroalkane chains in comparison to alkane chains, thus explaining the large increases in free volume with increasing temperature in the polymer matrix observed in this work. A discontinuity with regard to both solubility and clustering behavior was observed for a polymer carbon number of 10 to 12 carbon atoms. Prior work on the energy contributions towards the helical structure of perfluoroalkanes showed a shift in the energy contribution regime for carbon numbers larger than ~10 carbon atoms, which may explain this discontinuity. It was found that linear water clusters accounted for up to ~90 percent of the water clusters, concurring with previous work on water clustering in polyethylene.
Unlike interactions in simulated methane clathrate hydrates.
(2014) Lasich, Matthew.; Ramjugernath, Deresh.; Mohammadi, Amir Hossein.; Bolton, Kim.; Vrabec, J.
Clathrate hydrates are an ice-like substance consisting of networks of water molecules, held together by hydrogen bonds, enclosing trapped gas molecules. Natural gas clathrate hydrates (in which the trapped gas species is chiefly methane) are of interest in the field of offshore gas exploitation, where they frequently form blockages in natural gas pipelines. Knowledge of the phase equilibria of methane clathrate hydrate can thus reduce the overall monetary cost of natural gas extraction. Computer simulation of molecular systems is useful to understand fundamental mechanisms, and serves as a complementary method to laboratory experiments in the study of chemical systems. The Lennard-Jones potential is frequently used to describe intermolecular interactions in molecular simulations. Correction factors are often applied to the Lennard-Jones potential, although the effect of these correction factors on the behaviour of simulated molecular systems is not fully understood. This thesis examines the effect of Lennard-Jones correction factors on simulated methane clathrate hydrates using three different computational approaches: lattice distortion theory, grand canonical Monte Carlo simulations (which emulate gas adsorption into the clathrate lattice), and direct estimation of the heat of dissociation coupled with the Clausius-Clapeyron equation. In addition, the use of the results of grand canonical Monte Carlo simulations to infer phase equilibria was demonstrated in this thesis. The application of Lennard-Jones correction factors in lattice distortion calculations was found to not be viable, due to the extreme sensitivity of the perturbation potential (the quantity of interest in this theory) to changes in the values of the correction factors. Unlike interactions were found to weakly influence methane adsorption into the clathrate hydrate crystal, and so the application of correction factors in grand canonical Monte Carlo simulations is demonstrated to be ineffectual. The direct estimation of the heat of dissociation was shown to be viable when matching to calorimetric data, and the inference of phase equilibria by coupling the Clausius-Clapeyron equation with this approach was shown to yield agreeable results.